LFP on Shore Power with Inverter/charger?

[BFL13]

An inverter/charger requires that you have a battery connected (or some 12v source) so it will supply any 12v to the RV. (Unlike a converter that will do 12v with no battery)

Some say not to float an LFP. If you choose not to float yours, what do you do when on shore power? You can't isolate the battery and run 12v off the charger in the inverter/charger since it would be dead.

You could just not enable the charger, and run 120v off shore power pass through---or can you? Does 120v pass-through happen with no 12v to the inverter/charger?--- And just cycle the LFP for your 12v, thus not floating it.

What do folks do in that situation?

[FWC]

BFL13 wrote:
IMO that does not pin the thing down---nailing Jello to the wall and all that. It is all too wishy-washy for me.

If I had one, I would get it as full as I could (won't take any more amps) and then run one of my capacity tests. If I assumed 120AH is full, I would run it down at 6 amps for 10 hrs and note the Trimetric monitor's AH counter. If it came to 60 amps in 10 hrs I would say it is indeed a 120AH batt.

If it came to 55 AH, I would say it is a 110 AH batt. Whatever it came to, I would use that as my capacity for monitoring it. ( I might have to run another test at 5.5 amps to be accurate) I would adjust the capacity for temperature like I do now, so I have a pretty good idea what I have in the bank while camping. At least I would feel like I have a real number.

I don't like how you can't measure an AGM with an hydrometer, but at least you can use the AH count and compare that with voltage to see if they "match". LFPs are even worse it seems! Now you can do the AH count, but can't easily "match" that to a voltage. Phooey. I like to cross check to verify meters and gauges.

You guys can sort it all out to suit yourselves, which is how it is supposed to be. Meanwhile, I can keep on with my Fred Flintstone methods. 🙂

This makes zero sense. Your 'capacity test' would only tell you that the battery has a capacity > 60Ah. It would not tell you anything about what the actual capacity is. Furthermore, if you pull 6A for 10 hours, your trimetric will show 60Ah regardless of battery capacity, not 55Ah.

[BFL13]

FWC wrote:
PS the resting or 'nominal' voltage of LiFePO4 is NOT 13.6V. The resting voltage is 13.2 - 13.3 and the 'nominal' voltage is 12.8V.

BB says 13.6 is "full" and 13.3 is more like 90%, but whatever. Everyone seems to agree that 10v is "depleted". They should agree on "full" too. Why don't they? I know different brands of FLA and AGM don't agree, but they do give out their own tables so you can use the right numbers for what battery you have.

[BFL13]

IMO that does not pin the thing down---nailing Jello to the wall and all that. It is all too wishy-washy for me.

If I had one, I would get it as full as I could (won't take any more amps) and then run one of my capacity tests. If I assumed 120AH is full, I would run it down at 6 amps for 10 hrs and note the Trimetric monitor's AH counter. If it came to 60 AH in 10 hrs I would say it is indeed a 120AH batt.

If it came to 55 AH, I would say it is a 110 AH batt. Whatever it came to, I would use that as my capacity for monitoring it. ( I might have to run another test at 5.5 amps to be accurate) I would adjust the capacity for temperature like I do now, so I have a pretty good idea what I have in the bank while camping. At least I would feel like I have a real number.

I don't like how you can't measure an AGM with an hydrometer, but at least you can use the AH count and compare that with voltage to see if they "match". LFPs are even worse it seems! Now you can do the AH count, but can't easily "match" that to a voltage. Phooey. I like to cross check to verify meters and gauges.

You guys can sort it all out to suit yourselves, which is how it is supposed to be. Meanwhile, I can keep on with my Fred Flintstone methods. 🙂

[FWC]

PS the resting or 'nominal' voltage of LiFePO4 is NOT 13.6V. The resting voltage is 13.2 - 13.3 and the 'nominal' voltage is 12.8V.

[FWC]

Nominal means at least 120Ah, it is specified to be at least 120Ah, but may be more. Same deal with 12.8V "nominal" - they are estimating Wh by multiplying the nominal voltage by the nominal Ah. The battery will provide at least this amount on energy, practically it will provide more, as the voltage will be 13.2 - 13.3V for 95% of the discharge curve. As long as the battery beats the ratings, then no one will complain.

They don't specify the time frame for the Ah rating, but it doesn't really matter for lithium as Peukert is about 1.0 anyway.

[BFL13]

FWC wrote:
You would want to enter 120Ah for your 120Ah battery, as it states clearly in the spec sheet.

FWC, the spec sheet says 120AH "nominal" It gives the capacity as 1536 Wh without saying, "nominal". It says the 12.8v is "nominal". So why do you believe the "real" capacity is 120AH? If it is, then the Wh figure is wrong AFAIK. (13.6 is full, not 12.8)

Do you believe or know that they measured its capacity as 120AH first, then derived that 1536 Wh figure afterwards from the nominal 12.8 voltage?

If so, how do you think they got that 120AH? By running it at 120a for 1 hour? Or how? The usual 20 hr rate test ends at 10.5a but these batts are "depleted" at 10a. Not sure that works.

Be very interested in your explanation, thanks.

[FWC]

You would want to enter 120Ah for your 120Ah battery, as it states clearly in the spec sheet.

[jaycocreek]

My last charge that I re-synced the battery as 100% full was with a Lifepo4 battery charger from Expert Power whom makes batteries also...The charger light turned to green from red and shut off..So I guess it was full..lol

I doubt in my use boondocking that I'll ever let it get below 30-40% because of charge time on the generator if solar isn't there...I camp in heavy timber mostly getting firewood and finding a sunny spot isn't a given..

[3_tons]

When you sync your meter make sure that the battery is fully charged and that cell balancing has been completed...This will be the case (post balancing act) once the voltage is holding steady at 14.x and the current is resting at zero...

3 tons

[jaycocreek]

I turned the auto sync off and I'll go set the amp hours to 113...

Thanks

[3_tons]

Lynx states that the 120a/h = nominal capacity, though it’s not clear what that suggest - there may be a slight reserve beyond that??

3 tons

[BFL13]

IMO the 120AH capacity entry is too high, being based on the 12.8v instead of 13.6v

With the capacity too high, when it gets down to say 30% in its mind, you will be lower than that. I don't know how low you would ever go so that would put you "too low".

I see the video shows how you can set "alarms". I don't know how you get the alarm if you are not watching the cell phone or what you do there.

I would use 113AH as mentioned to be on the safe side. I know the BMS will shut it down at 10v, but then you lose all 12v, which might be a problem or not until you get it going again. I guess you could set the alarm for before it got that low. Combined with using a lower AH capacity like 113AH , that should keep you in the clear?

[3_tons]

I would disable ‘battery starts synchronized’ else wheneveryou disconnect then reconnect the battery, the meter will assume it’s at 100% and sync to 100% at whatever the last SOC was...

Congrats on a quality meter 🙂

3 tons

[jaycocreek]

I just took this..
I took a combination of Battleborn and Will Prowse's settings...I realize the 14.4 volts will make a difference instead of 14.6 but I don't quite understand that...lol..Any suggestions on my settings are very welcome..

[time2roll]

I would focus on 40% with LFP. 13.1v is 40% and 13.2 is 70% so you have this relatively slow drop to 13.1 and then it starts dropping 10% for every .1 volt.

Again the voltmeter is going to be a good indication of charge level. The whole 50% thing is a lead-acid hangover. Even at 40% there is a long way to go before recharge is critical.